1. Field of the Invention
The present invention is related to the packaging of light-emitting diode that mainly uses silicon wafers as the packaging substrates. Silicon wafers with (100) or (110) crystallization orientation can be etched to form minute groove reflectors. Oxidation treatment can provide good electrical insulation effect. Besides, the packaging process uses silicon rubber dipping (heat resistance up to 200xc2x0 C.) and does not need a molding process. The present invention has advantages such as high heat resistance, easy production of groove reflector, good heat dissipation, easy miniaturization, so it is much better than traditional SMD LED.
In the present invention, the method of producing grooves on silicon wafers and placing LED chips in the grooves has never been invented before. The present invention has integrated semiconductor micro-machine optoelectronic processing technology into the production of xe2x80x9csilicon substratexe2x80x9d specialized for LED, which changes the packaging structure that is based on a combination of traditional PC board, metallic leadframe and xe2x80x9cEpoxyxe2x80x9d resins. The present invention not only increases the reliability of SMD LED components but also shortens the production process and creates advantages such as high yield and high market competitiveness.
2. Description of the Prior Art
Presently, the packaging of surface mount devices of light-emitting diodes (SMD LED) is mainly divided into circuit type and leadframe type. Wherein, the SMD LED of leadframe type process uses metallic leadframe as substrates and injection molding for plastic grooves or compression molding, followed by cutting into SMD LED, as shown in FIG. 1. The SMD LED of circuit type uses composite circuit board as substrates, followed by compression molding and cutting into SMD LED, as shown in FIG. 2. So far, the SMD LED produced by the two methods has a common shortcoming, i.e. insufficient heat resistance. Especially when SMD components connected with board circuits are passing through high temperature furnace (at about 250xcx9c300xc2x0 C.), the packaging resin for SMD LED does not have sufficient heat resistance. Usually, since the packaging resin has Tg of only about 120xc2x0 C. and has a different coefficient of thermal expansion from that of the substrates or the leadframes, unusual defects often happen to SMD LED after its passing through high temperature furnace. Another shortcoming is poor heat dissipation. This is due to poor thermal conductance of the packaging resins and substrates. Besides, LED itself is a small heat-generating object, so the temperature increase due to poor heat dissipation will affect emitting efficiency and quality. A further shortcoming is the emitting intensity from the miniaturization without groove reflector has been reduced by more than one-fold (comparison at emitting angle of 30 degree), because it is difficult to use traditional process to make groove reflectors for SMD LED with dimensions of 0603 (1.6xc3x970.7 mm) and 0402 (1.0xc3x970.5 mm). Poor heat resistance, poor heat dissipation and difficulty in making minute groove reflectors are still the biggest problems for traditional SMD LED and have existed for more than twenty years.
After a long time research and development in the field of LED, the present invention has obtained many patents. A solution aiming at the above shortcomings for traditional SMD LED is proposed for improvement along with the present invention of xe2x80x9cPackaging of Light-Emitting Diodexe2x80x9d.
LED Silicon Substrate Process (A)
1. Select silicon wafers with (100) crystallization orientation (six inches).
2. Apply photoresist and remove unnecessary photoresist by exposure and development.
3. Use anisotropic wet etching to a certain depth and form grooves with declining surface of 54.74 degree (reflectors).
4. On the back of silicon wafers, use dry etching or laser treatment to make penetrating electrode holes.
5. Through oxidation or nitrogenation, form a layer of insulative SiO2 layer or Si3N4 layer.
6. Plate metallic layers (silver plating, including electrode layer on back of groove reflector).
7. Use laser (Nd-YAG) treatment to cut electrodes in grooves into positive and negative ends.
For etched grooves on silicon substrates, KOH is mostly used as the special wet etching material. When basic KOH is used for etching, since general photoresist will be etched by KOH, it needs to select special photoresist solution, i.e. solution for acidic development. (This type of photoresist is hard to buy in the market.) Another process (B) is necessary when general photoresist is used for etching silicon substrate.
LED Process (B)
1. Select silicon wafers with (100) crystallization orientation.
2. Form a layer of Si3N4 by heating in nitrogen high temperature furnace.
3. Apply photoresist followed by exposure and development.
4. Use reactive ion etching (RIE) to remove Si3N4 layer (hard mask) (also called stripping).
5. Use wet etching solution (KOH) to make groove structure.
6. Apply photoresist on the back of silicon wafers, followed by exposure and development.
7. Use RIE plasma etching to remove Si3N4 layer.
8. Use induction coupling plasma (ICP) for dry etching to make penetrating electrode holes.
9. Through oxidation and nitrogenation treatment for silicon wafers, form an insulative layer on groove surface.
10. Metallic Plating
11. Use laser treatment to cut the grooves into positive and negative ends.
The most apparent difference between A process and B process is that B process uses general photoresist while A process uses acidic development photoresist. In B process, a Si3N4 layer is formed first, which is then etched by RIE plasma. (RIE etches Si slowly. For another dry etching of Si, ICP will be used.) The above procedures describe the basic process to package silicon substrates of SMD LED in the present invention. For the wet etching of silicon substrate with (100) crystallization orientation, the etching profile is not vertically downward, but a groove of a declining angle of 54.74 degree, which is just suitable as the emitting angle of SMD LED. The formed groove can be applied to small angle SMD LED devices.
Fix LED chips in grooves of silicon substrate, followed by wiring, dipping, cutting into pieces of SMD LED, which accomplishes the first SMD LED device that uses silicon wafers as substrates with high heat resistance, good heat dissipation, small volume and strong emitting intensity.